6-ether substituted 1, 2, 3, 4-tetrahydroalkylquinolines



e-mnan SUBSTITUTED 1,2,3,4-TETRAHYDRO- ALKYLQUINOLINES,

James 0. Harris, St. Albans, W. Va., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application July 27, 1953 Serial No. 370,615

Claims. 260-289) This invention relates to new and useful compositions of matter. More particularly it relates to 6-ether substituted1,2,3,4 tetrahydroalkylquinolines.

One of the major problems of the rubber industry is the protection of rubber (natural and synthetic) goods against exposure cracking, that is degradation due to "ozone while the rubber article is under either static or dynamic stress. The problemis a difficult one and is aggravated by' the fact that in general chemical anti-oxidants or'age-fretarders have little or no value in protecting against deterioration by ozone. Although many materials have been suggested, such as the various waxes, factice, cellulose and the like to prevent ozone from reaching the rubber surface, not one. has been found entirely satisfactory. Accordingly rubber technologists" have constantly sought improvements. v I

In accordance with this invention it has been found that 6-ether substituted 1,2,3,4etetrahydroalkylquin'olines of the general formula I R/ s on:

where R is a hydrocarbon radical such as methyl, ethyl, propyl, isopropyl, butyl, amyl, o ctyl, dodecyl, benzyl, phenethyl, hexahydrobenzyl, cyclohexyl, phenyl, tolyl, ptert-butyl phenyl, naphthyl, and the like and where R and R" are the same or different short chain alkyl radicals such as methyl, ethyl, propyl, butyl, etc, or R" is hydr'ogen are a new family of valuable compounds. The new compounds are particularly effective anti-exposure cracking agents for natural and synthetic rubber goods. Of the new compounds 6-ether substituted 2,2,4-trialkyl-l,2,3,4-

tetrahydroquinolines wherein the 2,2,4-substituents are methyl radicals and the ether group is an alkoxy radical containing from 1 to 4 carbon atoms are particularly eifective in the control of exposure cracking and represent a preferred embodiment of this invention.

The new anti-exposure'cracking agents provided by this invention are the products of the hydrogenation of the corresponding 6'-eth er' substituted 2,2,4-trialkyl-L2-dihydroquinoline with an equimolecular amount of hydrogen in the presence of an effective hydrogenation catalyst, such as platinum, palladium or finely divided nickel. The hydrogenation may be conducted in the presence or absence of a saturated solvent incapable of being hydrogenated. Examples of operable solvents are cyclohexane and lower aliphatic acids. The reaction is usually carried out at temperatures between room temperature and 200 C. and hydrogen pressures of from 300 to 700 pounds per square inch gauge pressure, however it may be accomplished at lower or higher temperatures and pressures. The extent of the hydrogenation may be readily followed by observing the decrease in pressure as hydrogen is consumed. The hydrogenationreaction is preferably continued until hydrogen has been consumed in an amount corresponding approximately to that theoretically required for conversion of the, 1,2-dihydroquinoline to the l,2,3,4tetrahydroquinoline.

The 6-ether substituted 2,2,4-trialkyl-1,2-dihydroquinoline reactants employed in preparing the new compounds of this invention are obtained by condensing a para-ether substitutedaniline with amethyl ketone CH3-(|'|JR in a molar ratio of at least 1:2 in the presence of a suitable catalyst, e. g. iodine or bromine. It is now generally accepted that the condensation products of such primary amines with such methyl ketones are 1,2-dihydroquinolines of the strueture R and R having the same significance as aforedescribed. As illustrative of the preparation of thenew compounds of this invention are the following:

EXAMPLE 1 In a pressure autoclave 35.0 parts by weight (substantially 0.16 mole) of 6-ethoxy-2,2,4-trimethyl-l,Z-dihydroquinoline (B. P. 123125 C./2 mm.) was dissolved in parts by weight of methanol and 7 parts by weight of a 60% by weighf'suspens'ion of finely divided nickelin mineral oil wvas incorporated therein as the catalyst. While constantly agitating at room temperature and maintaining a pressure in the range of 450-6 35 pounds per square inch, hydrogenwas admitted to the mix over a period of about 45 minutes. The temperature rose gradually to about 125 C. 'Thereupon the reaction mix was removedand filtered and thesolvent removed-by evaporation. 35.3 parts by weight of a light yellow liquid possessing a boiling point of l22 C./2 mm., believed to be 6-ethoxy-2,2,4 -trimethyl-l,2,3,4-tetrahydroquinoline, was obtained.

EXAMPLE 2 Iutoa reactor of suitable capacity was charged 66 parts by weight (0.3 molecularfproportion) of 6-ethoxy,-2,2,4- tr'imethyl-l,2,3,4 tetrahydroquinoline, 42.6 parts by weight (0.3 molecular. proportion) of methyl iodide, 35.4.parts by weight ofsodium carbonate and 354 parts by weight of water. The, mixture was heated to refluxing temperature for about 6, hours and the organic layer separated. There was also formed. a small amount of a solid by-product insoluble' in both benzene and'water. This was probably the quaternary salt. Thebenzene soluble portion of the organic layerwas distilled under reduced pressure. 58.5 parts by weight of S-ethoxy-l,2,2,4-tetramethyl-l,2,3,4- tetrahydroquinoline 'was obtained, B. P. 144-153 C./2 mm., n =l.541 8.

The following examples in tabular form are presented to illustrate the variety of new 1,2,3-,4-tetrahydroquinolines which are prepared in 'accordancwith the invention.

Products of the reaction of hydrogen with a 6-ether substituted 2,2,4-triulkyl-],2-dihydrquinoline Dihydroquinoline Product visually at various intervals noting the extent of cracking. A stock which is severely cracked has no service the customary fashion and the respective compounded stocks cured in a press at 142 C. for 30 minutes. Since evaluation under static conditions is not indicative of the service obtained with many types of rubber articles which must withstand flexing, the vulcanized compositions were evaluated under dynamic conditions in an atmosphere containing a definite concentration of ozone. Samples of the stocks were cured in the form of a belt /2" wide, A thick and diameter and mounted on 1" diameter shafts. The ozone'concentration was maintained at 30 parts per hundred million throughout the test and the shafts were rotated at 75 R. P. M. In this manner a momentary elongation through a range of 02()% was provided at any portion of the test specimen passing over the shaft. (The apparatus and procedure employed is described in a paper of Creed et a1. entitled An Apparatus for the Evaluation of Ozone Protective Agents for Elastomers under Dynamic Condiy l y g g fi igl A-t F Y JJA- 5 life remaining in terms of- .theuseful life of a rubber y roquino me. e a y roqumo me. fiqsqmopoxyz 2, 4 t i th 1 1 fiqsopmpoxyqy 2, 4 t i th1 article and where the cracking is designated as extremely 6 y 0qu; i th 112 6 v igg i g severe'the degradation is well beyond even this point.

"ggfifgg g g "fgfgffi gg, ,g i g The results of the tests are set forth below: 6-n-butoxy-2, 2, 4-trirnethyl-1, 2- 6-n-but0Xy-2, 2, 4-trimethyl-I, 2, 3, 4- 'TABLE I dihydroquinoline. tetrahydroquinoline. 10 fi-n-hexoxy-Z, 2, 4-trimethyl-l, 2- 6-n-hexoxy-2, 2, 4-trimethyl-I, 2, 3, 4- dihydroquinoline. tetrahydroquinqline. Surface Cracking after Flexing in Ozone for- 6-benzoxy-2, 2, 'trimethyl-l, 2- 6-benzoxy-2, 2, 4-trimethy1-1, 2, 3, 4- Stock dihydroquinoline. tetrahydroquinoline. 6-naphthoxy-2, 2, 4-trimethyl-l, 2- 6-naphthoxy-2, 2, 4-trimethyl- 8 hrs. 32 hrs. 48 hrs. 96 hrs.

dihydroquinoline. 1, 2, 3, i-tetrahydroquinoline. 6-be11zyloxy-2, 2, 4-trin1ethyl-l, 2- G-benzyloxy-Z, 2, 4-trimethyl- 1 5 dihydroquinoline. .1,2,3,4-tetrahydr0qwn01 e. A slight extremely extremely 6-methoxy-2, 4-diethyl-2-rnethyl- 6-methoxy-2, 4-diethyl-2-methylr s v r l,2dihydroquinoline. 1,2,3,4tetrahydroquinoline- B none very slig slight G-ethoxy-Z, 4-diethyl-2-mcthyl-1, 2- fi-ethoxy-Z, 4-diethyl-2-methy1- v 0 very slight..-

dihydroquinoline. 1, 2, 3, 4-tetrahydroqu nolme. (1 none. moderate. 6-ethoxy-2,4-di-n-propyl-2-methyl- 6-ethoxy-2,4-di n-propyl-2-methyldo slight. 1, Z-dihydroquinoline. 1, 2, 3, 4-tetrahydroquinoline. 6-ethoxy-2,4-di-isopropyl-2- 69ethoxy-2,4-di-isqpropyl-2-niethyl 2O y -q y q 6 y% q 1 The new compounds of this invention are. particularly ggiiiih riii igiigg y *i,2fi-emii r%u useful in the control of exposure cracking of the sulfur- -e l s gy-l t y r g y y 1 'iif ?n y v |4' vulcanizable synthetic rubber-hke materials prepared by 1'0 1111101118. e ['3 y oqu 0 V G atuity-2P2,4-trimethy1-1,2-dihy- 6-amoxy-2,2,4-trimethyl-l, 2, 3, 4- h rolymerlzatwg of a coniugatedv dlene compound, 6 g gq p g- 4t th 11 2 6 ggg iigi g g fi 1 either alone. or with other unsaturated compounds co- ;,,gg i g fi i g g polymerizable therewith. The synthetic rubbers which may be substantially improved in ozone resistance are The anti-exposure cracking properties of the 6-alkoxy polymers of aliphatic conjugated dienes such as buta- 2,2,4-trirnethyl-1,2,3,4-tetrahydroquinolines are very simdiene, isoprene, ethyl butadiene, piperylene, dimethyl ilar regardless of the size of the alkoxy group, at least butadiene, and the like either alone or with unsaturated for the range of 1-12 carbon atoms. Furthermore, the monoolefinic compounds which contain the CH =C replacement of the hydrogen on the nitrogen atom by group such as the vinyl aromatics, namely styrene, a short chain alkyl group in the above identified products czmethyl styrene, nuclear substituted styrenes, monostill retains the antiexposure cracking properties characchlorstyrene, dichlorstyrene, divinyl benzene, vinyl naphteristic of the class although the tetraalkyl derivatives thalene, vinyl biphenyl, vinyl carbazole, 2-yinyl-5-ethyl are somewhat inferior to the trialkyl derivatives. pyridine, etc., and such vinyl compounds as acrylonitrile, As illustrative of the anti-exposure cracking properties methacrylonitrile, acrylic acid, methacrylic acid, methyl in natural rubber vulcanizates of the new compounds of vinyl ketone, and the hke.. this invention, rubber compositions were prepared utiliz- As Illustrative of the control of exposure crackingof ing the following ingredients: 4 vulcamzed sulfur-vulcanizable synthetic rubber-like materials, a rubbery butadiene-l,3-styrene copolymer com Stock A B O D position was prepared utilizing the following ingredients:

Parts by weight Struck F G H J Smoked sheets rubber 100 100 100 100 100 Carbon black 50 5o 50 50 Parts by e i Saturated hydrocarbon softener- 3 3 3 3 3 211m oxide 5 5 5 5 5 GR-S 10o 100 100 100 '100 Ste m fi 3 3 3 3 3 Carbon black 50 50 50 50 Sulfur 2.5 2.5 2.5 2.5 2.5 10 10 1o 10 N-Oyclohexyl-Z-benzothiazole sul- 4 4 4 4 fenamide 0.8 0.8 0.8 0.8 0.8 2 2 2 2 e-Etiiox -2,2,4-trimethy1-1,z-dihydro- Sulfur 1.75 1.75 1.75 1.75 qumolin 1 N-Oyclohexyl-Z-benzothlazdle sulfenamide-.- 1.2 1.2 1.2 1.2 fiy t y G-Ethoxy- 2,4-trimethyl-l,2rdihydrotetrahydroqumolme. quinoline 1 1.5

6-]?tdli oxy-zfA-trimethyl-l,2,3,4-tetra- 1 -12-dh (1r ujn line s a well-hi wn anti- Y 011111110 1119 1.5 gglffiffifi g gfi 1 y 1 6-Ethoxy-1,2,2,4 -tetramethyl-1,2,3,4-

tetrahydroquinoline 71.5 The ingredients were admixed on a rubber mill in 1 6-etl1oxy-2,2,4-trimethyl-1,2-dihydroquinoline is a well-known antiexposure cracking agent.

The ingredients were admixed on a rubber mill in the customary fashion and the respective compounded stocks cured in a press at 144 C. for 30 minutes. The vulcanizates were then evaluated for cracking resistance as aforedescribed. The resultsof the tests are setforth below:

- TAB LE II Surface Cracking after Flexing in Ozone for- Stock 8 hrs. 32 hrs. 56 hrs.

F none. extremely severe extremely severe.

very slight moderate.

very slight. slight.

While the invention has been described with respect to certain specific embodiments it is not so limited and it is to be understood the variations and modifications thereof obvious to those skilled in the art may be made without departing from the spirit or scope of this invention.

This application is a continuation-in-part of application Serial No. 308,913, filed September 10, 1952.

What is claimed is: p

1. As new compounds 6-ether substituted 1,2,3,4- tetrahydroquinolines of the structure where R is a hydrocarbon radical containing less than 13 carbon atoms and R is an alkyl group containing less than 5 carbon atoms and R" is selected from a group consisting of alkyl groups containing less than 5 carbon atoms and hydrogen.

2. As new compounds 6-ether substituted 2,2,4-trialkyl-1,2,3,4-tetrahydroquinolines of the structure /C- R' on;

6 where R is a hydrocarbon radical containing less than 13 carbon atoms and where R is an alkyl group containing less than 5 carbon atoms.

3. As new compounds 6-alkoxy substituted 2,2,4-trimethyl-1,2,3,4-tetrahydroquinolines.

4. As new compounds 6-alkoXy substituted 2,2,4-trirnethyl-1,2,3,4-tetrahydroquinolines, the alkyl group of the alkoxy substituent containing from 1 to 4 carbon atoms inclusive.

5. As a new compound 6-ethoxy 1,2,2,4-tetramethyl- 1,2,3,4-tetrahydroquinoline.

References Cited in the file of this patent UNITED STATES PATENTS Dunbrook et al. June 11, 1940 Leffier et al. Aug. 28, 1951 OTHER REFERENCES 

1. AS NEW COMPOUNDS 6-ETHER SUBSTITUTED 1,2,3,4TETRAHYDROQUINOLINES OF THE STRUCTURE 